The present invention relates to an improvement in an electric power steering apparatus for an automotive vehicle.
As is well known, an electric power steering apparatus for an automotive vehicle has an electric actuator such as an electric motor to assist driver's steering operation by a rotational driving force of the electric actuator.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-189868 discloses one type of electric actuator for use in such an electric power steering apparatus, in which a motor control circuit board and an inverter power module (circuit board) are stacked and incorporated into a control unit. In this control unit, heat generating electronic components such as CPU for command processing, IC (ASIC) for power supply control, semiconductor switch (FETMOS) for motor control, motor relay (power supply relay) for fail safe control etc. are mounted on the circuit boards. There is thus a tendency that that the thermal load on the control unit increases with the amount of heat generated in the control unit.